The present invention relates to an electric discharge machine and a method of producing a nozzle body using the electric discharge machine.
Discharge is generated by applying voltage between an electrode and a work piece, thereby a hole is formed in the work piece. JP-A-H9-85536 or JP-A-2001-259933 describes such a technology for forming plural holes in a work piece by a single processing operation. Specifically, plural electrodes are moved toward the work piece, and pulse voltages are periodically impressed to the electrodes, at the same time.
However, in this case, discharge usually occurs between only one electrode and the work piece based on the timings of impressing the pulse voltages. Even if voltage is simultaneously impressed to all the electrodes, discharge occurs first between one best-conditioned electrode and the work piece, because electric states between the electrodes and the work piece are different from each other. Once discharge occurs between a certain electrode and the work piece, discharge does not occur between other electrodes and the work piece. It takes a long time to form all the holes in this situation.
JP-A-H5-104332 or JP-A-2000-167717 describes an electric discharge processing, in which a position of an electrode is controlled by a motor so as to produce an optimal discharge between the electrode and a work piece. An electric discharge machine has a discharge state detector circuit to detect a discharge state such as discharge voltage or discharge current between the electrode and the work piece. A first feedback control is performed for determining a movement amount of the electrode in accordance with a detection signal output from the discharge state detector circuit. The machine further has a position detector circuit to detect a position of the electrode using a rotary encoder, for example, so as to accurately realize the movement amount. A second feedback control is performed for controlling the motor based on a detection signal output from the position detector circuit.
However, the first feedback control is not sufficiently accurate, because the electrode may still being controlled by the motor at a timing when the discharge state is detected. Even if the movement amount is set using the discharge state detected at the old timing in such case, the position of the electrode is further moved at a new timing when the movement amount is indicated to the electrode. Therefore, the second feedback control is necessary because the accuracy of the first feedback control is not enough.